Transflective liquid crystal display device with no retardation layer on the transmissive regions, manufacturing method thereof and electronic apparatus

ABSTRACT

An upper polarizing plate is provided on the outer surface of an upper substrate, and a lower polarizing plate is provided on the outer surface of a lower substrate. Also, a retardation layer having a phase shift of a quarter wavelength, and a protective layer are provided in turn only on reflective display regions of the inner surface of the lower substrate so that with no voltage applied, the phase shifts of a liquid crystal layer in transmissive display regions and the reflective display regions are set to a half wavelength and a quarter wavelength, respectively. Therefore, the present invention provides a transflective liquid crystal display device having enhanced display brightness in a transmission mode and excellent visibility.

This is a Continuation of application Ser. No. 10/385,749 filed Mar. 12,2003 now U.S. Pat. No. 7,218,363. The disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a liquid crystal display device, amanufacturing method therefor, and an electronic apparatus.Particularly, the present invention relates to a construction of atransflective liquid crystal display device with excellent visibility,which is capable of a sufficiently bright display in both a reflectivemode and transmissive mode.

2. Description of Related Art

The related art includes a liquid display device to enable a display tobe viewed in the light by using external light, like in a previousrelated art reflective liquid crystal display device, and to enable adisplay to be viewed in the dark by using an internal light source. Theliquid crystal display device uses a display system for both areflective display and transmissive display so that the display systemcan be switched to the reflective display or transmissive displayaccording to ambient brightness, thereby permitting a clear displaywhile decreasing power consumption even in a dark environment. This typeof liquid crystal display device is hereinafter referred to as a“transflective liquid crystal display device,”. An exemplary related arttransflective liquid crystal display device includes a reflective filmthat includes a metal film of aluminum or the like and having lighttransmission apertures on the inner surface of a lower substrate so asto function as a transflective film. The liquid crystal display deviceincludes the metal film provided on the inner surface of the lowersubstrate, and thus has the effect of reducing or preventing theinfluence of parallax due to the thickness of the lower substrate, andreducing or color mixing, particularly, in a structure including a colorfilter. The liquid crystal-side surface of each of substrates, whichconstitute a liquid crystal display device, is hereinafter referred toas the “inner surface”, and the opposite surface is hereinafter referredto as the “outer surface”.

FIG. 7 shows an example of a transflective liquid crystal display deviceincluding this type of transflective film.

In a liquid crystal display device 100, a liquid crystal layer 103 issandwiched between a pair of glass substrates 101 and 102, atransflective film 104 having apertures 104 a, and a transparentelectrode 108 comprising a transparent conductive film of indium tinoxide (hereinafter “ITO”) are laminated on the inner surface of thelower substrate 101, and an alignment film 107 is formed to cover thetransparent electrode 108. On the other hand, a transparent electrode112 including a transparent conductive film of ITO or the like is formedon the inner surface of the upper substrate 102, and an alignment film113 is formed to cover the transparent electrode 112. Also, tworetardation plates 118 and 119 (functioning as a quarter-wave plate 120)and an upper polarizing plate 114 are disposed on the outer surface ofthe upper substrate 102 in that order from the upper substrate 102, anda quarter-wave plate 115 and a lower polarizing plate 116 are providedon the outer surface of the lower substrate 101 in that order.Furthermore, a back light 117 (illumination device) including a lightsource 122, a light guide plate 123 and a reflective plate 124 isdisposed below the lower polarizing plate 116. Each of the quarter-waveplates 115 and 120 is capable of changing linearly polarized light tosubstantially circularly polarized light within a certain wavelengthregion.

The display principle of the transflective liquid crystal display device100 shown in FIG. 7 is described below with reference to FIG. 8. FIG. 8shows only components necessary for describing the display principle ofthe liquid crystal display device shown in FIG. 7.

First, in a dark display, a voltage is applied to the liquid crystallayer 103 (on state) to create a state in which the liquid crystal layer103 has no phase shift. In a reflective display, light incident on thetop of the upper polarizing plate 114 passes through the upperpolarizing plate 114 to become linearly polarized light perpendicular toFIG. 8 on the assumption that the transmission axis of the upperpolarizing plate 114 is perpendicular to the drawing. Further, thelinearly polarized light passes through the quarter-wave plate 120 tobecome counterclockwise circularly polarized light, which then passesthrough the liquid crystal layer 103. Then, the circularly polarizedlight is reflected by the surface of the transflective film 104 providedon the lower substrate 101 to become clockwise circularly polarizedlight due to inversion of the rotation direction. Furthermore, thecircularly polarized light passes through the liquid crystal layer 103,and then passes through the quarter-wave plate 120 to become linearlypolarized light parallel to FIG. 8. Since the upper polarizing plate 114has the transmission axis perpendicular to the FIG. 8, reflected lightis not returned to the outside (observation side) due to absorption bythe upper polarizing plate 114, thereby causing a dark display.

On the other hand, in the transmissive display, light emitted from theback light 117 passes through the lower polarizing plate 116 to becomelinearly polarized light parallel to the drawing on the assumption thatthe transmission axis of the lower polarizing plate 116 is parallel tothe drawing. Then, the linearly polarized light passes through thequarter-wave plate 115 to become clockwise circularly polarized light,which then passes through the liquid crystal layer 103. Then, theclockwise circularly polarized light passes through the quarter-waveplate 120 to become linearly polarized light parallel to FIG. 8, whichis then absorbed by the upper polarizing plate 114 to cause a darkdisplay in the same manner as the reflective mode.

In a light display with no voltage applied to the liquid crystal layer103 (off state), a phase shift is set to a quarter wavelength by abirefringence effect of the liquid crystal layer 103. In the reflectivedisplay, light is incident on the upper polarizing plate 114 from above,and passes through the upper polarizing plate 114 and the quarter-waveplate 120 to become counterclockwise circularly polarized light, whichthen passes through the liquid crystal layer 103. Then, the circularlypolarized light reaches the surface of the transflective layer 104 tobecome linearly polarized light parallel to FIG. 8. Furthermore, thelinearly polarized light is reflected by the surface of thetransflective layer 104, and then passes through the liquid crystallayer 103 to become counterclockwise circularly polarized light, whichthen passes through the quarter-wave plate 120 to become linearlypolarized light perpendicular to FIG. 8. Since the upper polarizingplate 114 has the transmission axis perpendicular to FIG. 8, thereflected light passes through the upper polarizing plate 114 andreturns to the outside (observation side), causing a light display.

On the other hand, in the transmissive display, light emitted from theback light 117 passes through the lower polarizing plate 116 and thequarter-wave plate 115 to become clockwise circularly polarized light.Then, the circularly polarized light passes through the liquid crystallayer 103 to become linearly polarized light perpendicular to FIG. 8.The linearly polarized light perpendicular to the drawing passes throughthe quarter-wave plate 120 to become counterclockwise circularlypolarized light. Since the upper polarizing plate 114 has thetransmission axis perpendicular to the drawing, only linearly polarizedlight perpendicular to the drawing of the counterclockwise circularlypolarized light passes through the upper polarizing plate 114 to cause alight display.

A related art apparatus is disclosed in Patent Publication No. 3235102.

SUMMARY OF THE INVENTION

As described above, the liquid crystal display device 100 shown in FIGS.7 and 8 is capable of producing a visible display regardless of thepresence of external light, but has the problem of insufficient light ina transmissive display in comparison to a reflective display.

A cause of this problem is that, according to the display principledescribed above with reference to FIG. 8, in a transmissive lightdisplay, light incident on the upper polarizing plate 114 after passingthrough the liquid crystal layer 103 and the quarter-wave plate 120 (theretardation plates 118 and 119) is circularly polarized light, and thusabout a half of the circularly polarized light is absorbed by the upperpolarizing plate 114 and does not contribute to a display.

Another cause is that a part of light emitted from the back light 117does not pass through the apertures 104 a of the transflective layer 104and is reflected by the back of the transflective layer 104 to becomecounterclockwise circularly polarized light due to the inversion of therotation direction, and the counterclockwise circularly polarized lightpasses through the quarter-wave plate 115 to become linearly polarizedlight perpendicular to the drawing. The linearly polarized light isabsorbed by the lower polarizing plate 116 having the transmission axisparallel to the drawing. Namely, if a part of the light emitted from theback light 117 and not passing through the apertures 104 a passesthrough the lower polarizing plate 116 and returns to the back light 117without being absorbed by the lower polarizing plate 116, the returnlight is again emitted to the liquid crystal cell to effectively improvethe brightness of the back light 117. However, the light not passingthrough the apertures 104 a is actually reflected by the back of thetransflective layer 104 and then almost completely absorbed by the lowerpolarizing plate 116, thereby failing to reuse the light.

Furthermore, the liquid crystal display device shown in FIG. 7 requirespluralities of retardation plates and polarizing plates to be bonded toboth outer surfaces of a pair of substrates with a liquid crystal layersandwiched therebetween, and thus has the problems of complicating theconstruction, increasing the manufacturing cost, and failing to thin theliquid crystal display device.

Accordingly, the present invention addresses or solves the above and/orother problems, and provides a transflective liquid crystal displaydevice capable of both a reflective display and a transmissive display,and particularly a liquid crystal display device having excellentvisibility and enhanced display brightness in a transmissive mode, and amethod of manufacturing the same. The present invention also provides anelectronic apparatus including a liquid crystal display device havingexcellent visibility.

In order to address or achieve the above, a transflective liquid crystaldisplay device of the present invention includes a liquid crystal layersandwiched between opposed upper and lower substrates each of which hasdot regions each having a transmissive display region and a reflectivedisplay region, an upper polarizing plate provided on the outer surfaceof the upper substrate, a lower polarizing plate provided on the outersurface of the lower substrate, and a reflective layer and retardationlayer provided on the reflective display regions of the inner surface ofthe lower substrate in that order from the substrate side. With one of aselective voltage applied or a non-selective voltage applied, a phasedifference of the liquid crystal layer in the transmissive displayregions is greater than that in the reflective display regions.

Of some causes of a decrease in brightness of the transmissive display,in order to address or solve the cause that light emitted from a backlight is reflected by the back of a transflective layer, and absorbed bya lower polarizing plate, thereby failing to reuse the light, theapplicant filed a liquid crystal display device comprising a retardationlayer (quarter wavelength) provided only on transmissive display regionsof the inner surface of a lower substrate. In this construction, theretardation plate (quarter-wave plate) need not be provided between thelower substrate and the back light so that light reflected from the backof the transflective layer passes through the lower polarizing platewithout any change, is reflected by a reflective plate of the backlight, and then again enters the liquid crystal panel, therebypermitting the effective utilization of light from the back light.However, in this construction, the lower retardation plate is providedonly on the inner side of the liquid crystal panel without changes inthe constructions of an upper retardation plate and a polarizing plate,and changes in the display principle of a transmissive display.Therefore, the problem of darkening the transmissive display due to theabsorption of about a half of circularly polarized light by the upperpolarizing plate, and the problem of complicating the structure toincrease the number of necessary components remain unsolved.

Therefore, the inventors conceived a construction opposite to theabove-described construction, i.e., a construction in which aretardation layer is provided only on the reflective display regions ofthe inner surface of the lower substrate, and the phase difference ofthe liquid crystal layer in the transmissive display regions is greaterthan that in the reflective display regions so as to compensate a phasedifference applied only to the reflective display regions by theretardation layer. In this construction, the setting conditions, such asthe phase differences of the retardation layer and the liquid crystallayer, can be set to permit a transmissive display using only linearlypolarized light, thereby eliminating the need for the upper retardationplate as well as the lower retardation plate. As a result, it ispossible to address or resolve the problem of a related art constructionin which about a half of circularly polarized light is absorbed by theupper polarizing plate to darken the transmissive display, therebylightening the transmissive display as compared with the related artconstruction. It is also possible to simplify the structure and thin thedisplay device, as compared with a conventional display device. Thedisplay principle of the liquid crystal display device of the presentinvention is described below in the Detailed Description of PreferredEmbodiments section of this application.

As a method of setting the phase difference of the liquid crystal layerin the transmissive display region to be greater than that in thereflective display region, at least one of the thickness d of the liquidcrystal layer and the refractive index anisotropy Δn of the liquidcrystal in the transmissive display regions may be different from thatin the reflective display regions because a phase difference(retardation) is represented by the product Δn·d of the thickness d ofthe liquid crystal layer and the refractive index anisotropy Δn of theliquid crystal. However, it is difficult to actually greatlydifferentiate the refractive index anisotropy Δn of the liquid crystalin the transmissive display regions from that in the reflective displayregion. Thus, the thickness of the liquid crystal layer in thetransmissive display regions is easily set to be greater than that inthe reflective display regions.

The retardation layer gives transmitted light a phase shift of about aquarter wavelength, and thus the thickness of the liquid crystal layerin the transmissive display region is preferably about twice as large asthat in the reflective display region, so that with one of the selectivevoltage applied and the non-selective voltage applied, the phase shiftsin both the reflective display regions and the transmissive displayregions are substantially zero, and with the other voltage applied, thephase shifts of the liquid crystal in the reflective display regions andthe transmissive display regions are about a quarter wavelength and ahalf wavelength, respectively.

The “phase shift of a quarter wavelength” means that when linearlypolarized light is incident on an optical isomer (for example, theliquid crystal or retardation plate), emitted light becomes circularlypolarized light, and a “phase shift of a half wavelength” means thatemitted light becomes linearly polarized light perpendicular to incidentlinearly polarized light. A “phase shift of 0” or “no phase shift” meansthat emitted light becomes linearly polarized light parallel to incidentlinearly polarized light.

In this construction, in transmission through the upper polarizingplate, linearly polarized light in the reflective display can be putinto the same polarized state as that in the transmissive display, andthus the phase shift in the reflective display regions can be set tosubstantially the same as that in the transmissive display regions. Itis thus possible to enhance the utilization efficiency of light topermit a construction capable of a brightest transmissive display. It isalso possible to obtain a display with a high contrast.

The retardation layer may include a polymer liquid crystal.

In this construction, the retardation layer can be relatively easilyformed on the inner surface of a substrate.

Also, an insulating layer is preferably provided on the retardationlayer.

In the liquid crystal display device of the present invention,particularly when the retardation layer includes the polymer liquidcrystal, the insulating layer provided on the retardation layerfunctions as a protective film to prevent deterioration of theretardation layer. In the construction of the present invention, theretardation layer is provided only in the reflective display region, andthus the insulating film formed on the retardation layer permits therealization of a structure in which the thickness of the liquid crystallayer in the reflective display region is smaller than that in thetransmissive display region. For example, the thickness of the liquidcrystal layer in the transmissive display region can easily be set to beabout twice as large as that in the reflective display region bycontrolling the thickness of the insulating layer.

Like the above-described insulating layer, a liquid crystal thicknesscontrolling layer is preferably provided on the retardation layer, tocontrol the thicknesses of the liquid crystal layer in the transmissivedisplay region and reflective display region.

In this construction, by controlling the thickness of the liquid crystallayer thickness controlling layer, it is possible to easily realize astructure in which the thickness of the liquid crystal layer in thereflective display region is smaller than that in the transmissivedisplay region. For example, the thickness of the liquid crystal layerin the transmissive display region can easily be set to about twice aslarge as that in the reflective display region.

The retardation layer may function as the liquid crystal layer thicknesscontrolling layer to control the thicknesses of the liquid crystal layerin the transmissive display region and reflective display region.

Namely, the retardation layer is provided only in the reflective displayregion, and thus the retardation layer can be caused to function as theliquid crystal layer thickness controlling layer to decrease thethickness of the liquid crystal layer in the reflective display regionby controlling the thickness of the retardation layer. In thisconstruction, the liquid crystal layer thickness controlling layerincluding the insulating layer or the like need not be providedseparately, thereby simplifying the device structure and manufacturingprocess.

The rubbing axis of the upper substrate is preferably perpendicular orparallel to the transmission axis of the upper polarizing plate so thatwith the non-selective voltage applied, the liquid crystal molecules ofthe liquid crystal layer are twisted by about 90° between the upper andlower substrates.

In this construction, with the selective voltage applied or thenon-selective voltage applied, the phase shift in the transmissivedisplay region is a half wavelength or 0 due to rotatory performance.Namely, the transmissive display is a TN (Twisted Nematic) rotatory modedisplay using linearly polarized light, thereby enhancing theutilization efficiency of light, permitting a bright display andwidening a viewing angle.

In this construction, the retardation of the liquid crystal layer in thereflective display region is preferably 130 nm to 340 nm.

In the construction including the liquid crystal layer having such asmall retardation, with the selective voltage applied or thenon-selective voltage applied, the phase shift of the liquid crystallayer in the reflective display region is a quarter wavelength or 0 dueto insufficient optical rotation. Therefore, the visibility of thereflective display can be sufficiently secured. The reason to preferablyset the retardation in the above-described numerical range is describedbelow.

Furthermore, a reflective polarizing plate having a transmission axissubstantially parallel to the transmission axis of the lower polarizingplate is preferably provided on the outer surface of the lowerpolarizing plate.

When the reflective polarizing plate is not provided, a part of thelight emitted from the back light may be converted to linearly polarizedlight and absorbed by the lower polarizing plate. However, in thisconstruction, the linearly polarized light is reflected by thereflective polarizing plate to return to the back light, therebypermitting the reutilization of the light for the transmissive display.The reason why the linearly polarized light can pass through thereflective polarizing plate and contribute to a display is that thelinearly polarized light is repeatedly reflected by the reflectivepolarizing plate to change the polarizing axis direction, and is thusconverted to linearly polarized light in a direction different from theinitial direction. In this construction, the transmissive display can befurther brightened.

A method of manufacturing a liquid crystal display device of the presentinvention comprises the steps of forming a reflective layer on a regionof a lower substrate, which corresponds to a reflective display region,forming in turn a polymer liquid crystal layer and a photosensitiveresin layer, patterning the photosensitive resin layer by aphotolithography process, and then etching the polymer liquid crystallayer through the patterned photosensitive resin layer used as a mask tolocally leave the polymer liquid crystal layer, forming a retardationlayer including the polymer liquid crystal layer on the reflectivelayer.

Another method of manufacturing a liquid crystal display device of thepresent invention includes: forming a reflective layer on a region of alower substrate, which corresponds to a reflective display region,forming a layer including a liquid crystalline monomer, locallyoptically polymerizing the liquid crystalline monomer by aphotolithography process to form a liquid crystalline monomer polymer,forming a retardation layer including the liquid crystalline monomerpolymer above the reflective layer. The “liquid crystalline monomer”means a monomer that forms a liquid crystal phase by itself, or amonomer that does not form a liquid crystal phase by itself and does notlose the crystalline state of a mixture when being mixed in a liquidcrystal phase.

Any of the methods can relatively easily realize a structure in whichthe retardation layer is locally formed only in the reflective displayregion by a related art photolithography process. For example, thephotosensitive resin layer may be formed after the retardation layer isformed, and then patterned by the photolithography process to leave thephotosensitive resin layer above the retardation layer. This method caneasily realize a structure in which the thickness of the liquid crystallayer in the reflective display region is smaller than that in thetransmissive display region.

An electronic apparatus of the present invention includes theabove-described liquid crystal display device of the present invention.

In this construction, the electronic apparatus including a liquidcrystal display part exhibiting high brightness in a transmissivedisplay mode and excellent visibility can be provided.

The above-described operation and other advantages of the presentinvention will be made clear from the description of the exemplaryembodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the schematic construction of aliquid crystal display device according to a first exemplary embodimentof the present invention;

FIG. 2 is a schematic showing only components necessary illustrating thedisplay principle of the liquid crystal display device shown in FIG. 1;

FIG. 3 is a sectional view showing the schematic construction of aliquid crystal display device according to a second exemplary embodimentof the present invention;

FIG. 4 is a perspective view showing an example of an electronicapparatus according to the present invention;

FIG. 5 is a perspective view showing another example of an electronicapparatus according to the present invention;

FIG. 6 is a perspective view showing a further example of an electronicapparatus according to the present invention;

FIG. 7 is a sectional view showing the schematic construction of anexample of related art liquid crystal display devices;

FIG. 8 is a schematic showing only components necessary for illustratingthe display principle of the related art liquid crystal display device;

FIG. 9 is a sectional view showing the schematic construction of aliquid crystal display device according to a third exemplary embodimentof the present invention;

FIG. 10 is a sectional view showing the schematic construction of aliquid crystal display device according to a fourth exemplary embodimentof the present invention;

FIG. 11 is a sectional view showing the schematic construction of aliquid crystal display device according to another exemplary embodimentof the present invention;

FIG. 12 is a sectional view showing the schematic construction of aliquid crystal display device according to a further exemplaryembodiment of the present invention;

FIG. 13 is a graph showing the results of simulation for measuring acorrelation between Δn·d and reflectance in a reflective display regionof a liquid crystal display device of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described below withreference to the drawings.

First Exemplary Embodiment

A first exemplary embodiment of the present invention is described belowwith reference to FIGS. 1 and 2.

FIG. 1 is a sectional view showing the schematic construction of aliquid crystal display device according to this exemplary embodiment,and FIG. 2 is a schematic showing only components necessary illustratingthe display principle of the liquid crystal display device. Thisexemplary embodiment is an example of a transflective color liquidcrystal display device in an active matrix system. In all of thedrawings, the thickness and dimensional ratio of each component areappropriately changed to make each drawing more easily viewable.

As shown in FIG. 1, a liquid crystal display device 10 of this exemplaryembodiment includes a liquid crystal cell 11 and a back light 12(illumination device). The liquid crystal cell 11 comprises a lowersubstrate 13 and upper substrate 14, which are opposed to each other,and a liquid crystal layer 16 comprising a TN (Twisted Nematic) liquidcrystal or the like, which is sealed in the space between the uppersubstrate 14 and the lower substrate 13. The back light 12 is disposedat the back (the outer side of the lower substrate 13) of the liquidcrystal cell 11.

Also, a transflective layer 18 including a metal film having highreflectance, such as aluminum, silver, an alloy thereof, or the like, isformed on the inner side of the lower substrate 13 including a lighttransmitting material, such as glass or plastic. The transflective layer18 has apertures 18 a provided for respective pixels to transmit lightemitted from the back light 12. In the transflective layer 18, theregions each actually having the metal film include reflective displayregions R, and the apertures 18 a comprise transmissive display regionsT.

In each of the reflective display regions R, a retardation layer 20 anda protective layer 21 are laminated on the transflective layer 18 inthat order from the substrate side. The retardation layer 20 includes,for example, a polymer liquid crystal, and applies a phase shift of aquarter wavelength of visible light incident on the liquid crystal cell11. The protective layer 21 includes, for example, an insulating film ofan acrylic photosensitive resin, or the like.

The retardation layer 20 and the protective layer 21 can be formed by,for example, the following two exemplary methods.

In the first exemplary method, an alignment film material, SE-3140(trade name, produced by Nissan Chemical Industries, Ltd.) is firstcoated on the transflective layer 18 formed on the substrate by a spincoating process or flexographic printing process, burned, and thenrubbed. Then, a polymer liquid crystal solution is coated on thealignment film by a spin coating process (for example, for 30 seconds ata rotation speed of 700 rpm). The polymer liquid crystal solution usedis, for example, an 8% solution of PLC-7023 (trade name, produced byAsahi Denka Kogyo K. K.), and the solvent used is a mixture ofcyclohexanone and methyl ethyl ketone. The solution also has anisotropic transition temperature of 170° C., and a refractive anisotropyΔn of 0.21.

Next, the polymer liquid crystal layer is pre-baked at 80° C. for 1minute, further heated for 30 minutes at 180° C. higher than theisotropic transition temperature (170° C.) of the polymer liquidcrystal, and then gradually cooled to align the polymer liquid crystal.As a result of actual production under these conditions, the inventorsachieved a thickness of 630 nm, and a retardation of 133 nm.

Next, an acrylic photosensitive resin NN-525 (trade name, produced byJSR Co., Ltd.) is coated as a material for the protective layer by aspin coating process (for example, 30 seconds at a rotation speed of 700rpm). In this case, the thickness is 2.3 μm. Next, the protective layeris pre-baked at 80° C. for 3 minutes, and exposed to light through aphotomask (for example, an exposure strength of 140 mJ/cm², measured byan ultraviolet actinometer having sensitivity at 350 nm), and thendeveloped by dipping in an alkaline developer at room temperature for 90seconds to leave the protective layer only in the reflective displayregions. Since the acrylic photosensitive resin is a negative type, thephotomask must be formed so that the reflective display regions areexposed to light.

Next, in order to completely cure the protective layer, post-curing isperformed with an exposure strength of 2000 mJ/cm². With an exposurestrength of 1000 mJ/cm² or less, the protective layer peels indevelopment of the polymer liquid crystal in a next step, while with anexposure strength of 1300 mJ/cm² or more, no problem occurs. Therefore,the exposure strength is set to 2000 mJ/cm². Then, the polymer liquidcrystal is etched by dipping in an etchant comprisingN-methyl-2-pyrolizinone at room temperature for 30 minutes. Then, thesubstrate is dried at 80° C. for 3 minutes to form the retardation layer20 comprising the polymer liquid crystal and the protective layer 21including the acrylic photosensitive resin.

In the second method, an alignment film is formed on the substrate bythe same method as in the second method, and then a solution of UVcurable liquid crystal, UCL-008-KI (trade name, produced by DainipponInk And Chemicals, Incorporated), as a liquid crystalline monomer iscoated on the substrate by the spin coating process (for example, 30seconds at a rotational speed of 700 rpm). The liquid crystallinemonomer solution used is a 25% diluted solution in a mixed solventcontaining N-methyl-2-pylorizinone and r-butyrolactone, and has anisotropic transition temperature of 69° C. and a refractive indexisotropy Δn of 0.20.

Next, the liquid crystalline monomer is dried at 60° C. for 5 minutes,heated for 5 minutes at 90° C. higher than the isotropic transitiontemperature (69° C.), and then gradually cooled to align the crystallinemonomer. As a result of actual production under these conditions, theinventors achieved a thickness of 650 nm. Next, the liquid crystallinemonomer is exposed to light through a photomask (for example, anexposure strength of 3000 mJ/cm²) to locally optically polymerize thecrystalline monomer, and then developed by dipping in an alkalinedeveloper or a ketone-based organic solvent for 60 seconds to leave theliquid crystalline monomer polymer only in the reflective displayregions. Consequently, the retardation layer 20 including the liquidcrystalline monomer polymer is formed. Then, the protective layer 21 maybe formed on the retardation layer 20 by the same method as in the firstmethod.

In this way, in the liquid crystal display device 10 of this exemplaryembodiment, the retardation layer 20 and the protective layer 21 areprovided only in the reflective display regions R to form steps betweenthe reflective display regions R and the transmissive display regions T.Also, pixel electrodes 23 including a transparent conductive film of ITOor the like are formed along the steps, and an alignment film 24including polyimide or the like is formed to cover the pixel electrodes23. In this exemplary embodiment, the lower substrate 13 includes anelement substrate on which pixel switching elements each including TFTor the like, data lines, and scanning lines are formed. The pixelswitching elements, the data lines, and the scanning lines are not shownin FIG. 1. Furthermore, a lower polarizing plate 28 is provided on theouter surface of the lower substrate 13, and a conventional retardationplate is not provided.

On the other hand, a common electrode 32 including a transparentconductive film of ITO or the like, an alignment film 33 includingpolyimide or the like are laminated in order on the inner surface of theupper substrate 14 including a light transmitting material, such asglass or plastic. Also, an upper polarizing plate 36 is provided on theouter surface of the upper substrate 14, and a related art retardationplate is not provided. Although not shown in the drawing, a color filterincluding dye layers of R (red), G (green) and B (blue) is provided onthe inner surface of the upper substrate.

In the liquid crystal layer 16 sandwiched between the upper substrate 14and the lower substrate 13, the retardation layer 20 and the protectivelayer 21 are provided only in the reflective display regions R toproject toward the liquid crystal layer 16, so that the thickness of theliquid crystal layer in the reflective display regions R is differentfrom that in the transmissive display regions T. In this exemplaryembodiment, the thickness of the protective layer 21 is about 4 times aslarge as that of the retardation layer 20, and thus the thickness of theliquid crystal layer 16 is mainly controlled by the thickness of theprotective layer 21. More specifically, the thickness of the liquidcrystal layer 16 in the transmissive display regions T is about twice aslarge as that in the reflective display regions R. Also, a positivecrystal material is used for the liquid crystal layer 16, and therefractive index anisotropy Δn and thickness d of the liquid crystallayer are controlled so that with the selective voltage applied (voltageturned on), the liquid crystal molecules rise along the direction of anelectric field to cause a phase shift of 0 in the liquid crystal layer16 in both the reflective display regions R and the transmissive displayregions T, while with the non-selective voltage applied (voltage tunedoff), the liquid crystal molecules lie to cause a phase shift of aquarter wavelength in the liquid crystal layer 16 in the reflectivedisplay regions R, and a phase shift of a half wavelength in the liquidcrystal layer 16 in the transmissive display regions T. The rubbing axisof the upper substrate 14 is perpendicular or parallel to thetransmission axis of the upper polarizing plate 36, and the liquidcrystal molecules of the liquid crystal layer 16 are twisted by 90°between the upper substrate 14 and the lower substrate 13 when thenon-selective voltage is applied.

The back light 12 includes a light source 37, a reflective plate 38, anda light guide plate 39, and a reflective plate 40 is provided on thebottom (opposite to the liquid crystal panel 1 side) of the light guideplate 39, to emit light transmitted through the light guide plate 39 tothe liquid crystal cell 11.

Next, the display principle of the liquid crystal display device 10 ofthis exemplary embodiment is described below with reference to FIG. 2.

First, in a dark display, a voltage is applied to the liquid crystallayer 16 (with the selective voltage applied) to cause a phase shift of0 (no phase shift) in the liquid crystal layer 16. In the reflectivedisplay, light incident on the upper polarizing plate 36 from abovepasses through the upper polarizing plate 36 to become linearlypolarized light perpendicular to the drawing on the assumption that thetransmission axis of the upper polarizing plate 36 is perpendicular tothe drawing, and then passes through the liquid crystal layer 16 withoutany change. The linearly polarized light perpendicular to the drawing isprovided with a retardation of a quarter wavelength by the retardationlayer 20 provided on the lower substrate 13. After passing through theretardation layer 20, the linearly polarized light becomescounterclockwise circularly polarized light. Next, the circularlypolarized light is reflected by the surface of the transflective layer18 to become clockwise circularly polarized light due to the inversionof the rotational direction, and then again passes through theretardation layer 20 to become linearly polarized light parallel to thedrawing. The linearly polarized light then passes through the liquidcrystal layer 16 without any change. Since the upper polarizing plate 36has the transmission axis perpendicular to the drawing, the linearlypolarized light parallel to the drawing is absorbed by the upperpolarizing plate 36 without being returned to the outside (observationside), thereby creating a dark display.

On the other hand, in the transmissive display, light emitted from theback light 12 passes through the lower polarizing plate 28 to becomelinearly polarized light parallel to the drawing on the assumption thatthe transmission axis of the lower polarizing layer 28 is parallel tothe drawing, and then passes through the liquid crystal layer 16 withoutany change. The light is absorbed by the upper polarizing plate 36 tocreate a dark display in the same manner as the reflective mode.

Next, in a light display, a voltage is not applied to the liquid crystallayer 16 (with the non-selective voltage applied) to cause a phase shiftof a quarter wavelength in the reflective display regions R and a phaseshift of a half wavelength in the transmissive display regions T. In thereflective display, light passes through the upper polarizing plate 114to become linearly polarized light perpendicular to the drawing, andthen passes through the liquid crystal layer 16 to be provided with aphase shift of a quarter wavelength by the liquid crystal layer 16. Whenthe linearly polarized light passing through the liquid crystal layer 16reaches the surface of the retardation layer 20, it becomescounterclockwise circularly polarized light. Then, the circularlypolarized light passes through the retardation layer 20 to becomelinearly polarized light parallel to the drawing, and is then reflectedby the surface of the transflective layer 18 while maintaining itspolarizing state. Then, the light again passes through the retardationlayer 20 to return to counterclockwise circularly polarized light. Next,the light again passes through the liquid crystal layer 16 to return tolinearly polarized light perpendicular to the drawing, and then passesthrough the upper polarizing plate 36 having the transmission axisperpendicular to the drawing to return to the outside (observationside), thereby creating a light display.

On the other hand, in the transmissive display, light emitted from theback light 12 passes through the lower polarizing plate 28 to becomelinearly polarized light parallel to the drawing, and is then providedwith a phase shift of a half wavelength due to the rotatory performancepossessed by the liquid crystal layer 16. When the light passes throughthe liquid crystal layer 16, it becomes linearly polarized lightperpendicular to the drawing. The light then passes through the upperpolarizing plate 36 having the transmission axis perpendicular to thedrawing to return to the outside, thereby creasing a light display.

In the transmissive display, a part of the linearly polarized lightparallel to the drawing, which passes through the lower polarizing plate28, is reflected by the back of the transflective layer 18, passesthrough the lower polarizing plate 28 to return to the back light 12,and is reflected by the reflective plate 40 provided on the bottom ofthe back light 12 to be again emitted to the liquid crystal cell 11.Therefore, the light reflected by the back of the transflective layer 18can be again utilized to contribute to the transmissive display.

In the liquid crystal display device 10 of this exemplary embodiment,the retardation layer 20 having a retardation of a quarter wavelength isprovided only in the reflective display regions R of the inner surfaceof the lower substrate 13, and the thickness of the liquid crystal layer16 in the transmissive display regions T is about twice as large as thatin the reflective display regions R. Furthermore, with no voltageapplied, the phase shifts of the liquid crystal layer 16 in thereflective display regions R and the transmissive display regions T area quarter wavelength and a half wavelength, respectively. Therefore, thetransmissive display can be performed by using only linearly polarizedlight, thereby eliminating the need for the retardation plates providedon the top and bottom of the liquid crystal cell used in the related artdevice shown in FIG. 7.

In this construction, it is possible to simultaneously address or solveboth the problem of a related art construction in which about a half ofcircularly polarized light incident from the liquid crystal layer sideis absorbed by the upper polarizing plate to darken the transmissivedisplay, and the problem in which illumination light reflected by theback of the transflective layer is absorbed by the lower polarizingplate to fail to re-use the light for a display. Therefore, thetransmissive display can be brightened, as compared with a related artdisplay. In this embodiment, particularly, when the retardation in thetransmissive display regions T is twice as large as that in thereflective display regions R, polarized light before passing through theupper polarizing plate 36 can be set to linearly polarized light in thesame direction in the reflective display and the transmissive display.It is thus possible to enhance the utilization efficiency of light, andachieve a construction capable of a brightest transmissive display.Also, a display with a high contrast can be achieved. Particularly, inthis exemplary embodiment, the transmissive display is a TN mode displayusing linearly polarized light, thereby enhancing the utilizationefficiency of light, permitting a light display, and widening theviewing angle. Furthermore, even when the cell thickness in thetransmissive display regions varies and significantly increases to betwice or more (for example, 3 or 4 times) as large as the cell thicknessin the reflective display regions, a high-contrast display can beperformed because rotatory performance is utilized.

In this exemplary embodiment, the retardation layer 20 includes thepolymer liquid crystal, and an insulating film is formed on theretardation layer 20 so as to function as the protective film 21,thereby reducing or preventing deterioration in the retardation layer20. Also, the retardation layer 20 is provided only in the reflectivedisplay regions R, and thus the protective layer 21 formed on theretardation layer 20 permits the realization of a structure in which thethickness of the liquid crystal layer 16 in the reflective displayregions R is smaller than that in the transmissive display regions T.Furthermore, an outer retardation plate need not be provided to simplifythe structure, as compared with a related art construction. Therefore,the number of components can be decreased, and the display device can bethinned.

The inventors determined, by simulation, the correlation between thephase difference (retardation R=Δn·d) and reflectance in the reflectivedisplay regions of the liquid crystal display device of this exemplaryembodiment. FIG. 13 shows the simulation results. In FIG. 13, Δn·d [nm]is shown on the abscissa, and reflectance [−] is shown on the ordinate.In this exemplary embodiment, the transmissive display is a TN modedisplay to enhance the utilization efficiency of light and permits alight display. On the other hand, at least a reflectance of 20% or moreis required to achieve necessary brightness for the reflective displayin practical use. In order to obtain this level of reflectance, theretardation (Δn·d) in the reflective display regions must be set in therange of 130 nm≦Δn·d≦340 nm. By setting Δn·d in the reflective displayregions to satisfy the condition, the visibility of the reflectivedisplay can also be secured.

Second Exemplary Embodiment

A second exemplary embodiment of the present invention is describedbelow with reference to FIG. 3.

FIG. 3 is a sectional view showing the schematic construction of aliquid crystal display device of this exemplary embodiment. The liquidcrystal display device of this exemplary embodiment has the same basicconstruction as the first exemplary embodiment, but is different in thata reflective polarizing plate is added to the outer surface of a lowersubstrate. Therefore, in FIG. 3, the components common to those in FIG.1 are denoted by the same reference numerals, and a detail descriptionthereof is omitted.

As shown in FIG. 3, the liquid crystal display device 50 of thisexemplary embodiment includes a reflective polarizing plate 51 providedon the outer side of the lower substrate 13, and more specifically,provided on the outer side of the lower polarizing plate 28. Thereflective polarizing plate 51 has a transmission axis of linearlypolarized light in a predetermined direction, and the function toreflect linearly polarized light in a direction perpendicular to thetransmission axis. The reflective polarizing plate 51 is disposed sothat its transmission axis is substantially parallel to the transmissionaxis of the lower polarizing plate 28. As the reflective polarizingplate 51, for example, D-BEF (trade name, produced by Sumitomo 3M Ltd.),PCF (trade name, produced by Nitto Denko Corporation and disclosed inJapanese Unexamined Patent Application Publication No. 10-319235), orthe like can be used.

The liquid crystal display device 50 of this exemplary embodiment canexhibit the same effect as the first exemplary embodiment which iscapable of brightening the transmissive display, achieving a highcontrast display, decreasing the number of components, and thinning thedevice in comparison to a related art display device.

In the first exemplary embodiment, in the transmissive display, whenlight emitted from the back light 12 is incident on the lower polarizingplate 28, only linearly polarized light matching with the transmissionaxis of the lower polarizing plate 28 is transmitted, and other linearlypolarized light is absorbed and cannot be used for a display. On theother hand, in this exemplary embodiment, light emitted from the backlight 12 is incident on the reflective polarizing plate 51 before beingincident on the lower polarizing plate 28, and thus linearly polarizedlight, which is absorbed by the lower polarizing plate 28 in the firstexemplary embodiment, is reflected by the reflective polarizing plate 51before absorption, and can thus be re-used for the transmissive display.Therefore, in the construction of this exemplary embodiment, in thetransmissive display, the effect of reducing or preventing the lightemitted from the back light 12 from being absorbed by the lowerpolarizing plate 28 is combined with the same effect as the firstexemplary embodiment, i.e., the effect of reducing or preventing thelight passing through the liquid crystal layer 16 from being absorbed bythe upper polarizing plate 36, and the effect of permitting there-utilization of light reflected by the back of the transflective layer18 for a display. As a result, the transmissive display can be furtherbrightened in comparison with the first exemplary embodiment.

Third Exemplary Embodiment

A third exemplary embodiment of the present invention is described belowwith reference to FIG. 9.

FIG. 3 is a sectional view showing the schematic construction of aliquid crystal display device of this exemplary embodiment. The liquidcrystal display device of this exemplary embodiment has the same basicconstruction as the first exemplary embodiment, but is different in thata color filter for each of a reflective display and a transmissivedisplay is provided on a lower substrate. Therefore, in FIG. 9, thecomponents common to those in FIG. 1 are denoted by the same referencenumerals, and a detail description thereof is omitted.

As shown in FIG. 9, a liquid crystal display device 60 of this exemplaryembodiment includes a transflective layer 18 having transmissionapertures 18 a and provided on the inner surface of the lower substrate13, a reflective display color filter which is formed on thetransflective layer 18 and which has a dye layer 61R formed in thereflective display regions R, and a transmissive display color filterhaving a dye layer 61T formed in the apertures 18 a corresponding to thetransmissive display regions T. The dye layer 61R of the reflectivedisplay color filter is controlled to have lower chroma than that of thedye layer 61T of the transmissive display color filter. Also, aninsulating layer 62 including an acrylic resin or the like is formed onthe dye layer 61R of the reflective display color filter so as tofunction as a liquid crystal layer thickness controlling layer todecrease the thickness of the liquid crystal layer in the reflectivedisplay regions R as compared with that in the transmissive displayregions T. Furthermore, the same retardation layer 20 as in the firstembodiment is formed on the insulating layer 62, and the pixelelectrodes 23 and the alignment film 24 are laminated in turn on theretardation layer 20. The construction formed on the upper substrate 14is the same as in the first and second exemplary embodiments.

The liquid crystal display device 60 of this exemplary embodiment canexhibit the same effect as the first and second exemplary embodimentswhich are capable of brightening the transmissive display, achieving ahigh contrast display, decreasing the number of components, and thinningthe device in comparison to a related art display device. Furthermore,in the liquid crystal display device 60 of this exemplary embodiment,light passes twice through the color filter in the reflective displayregions R, while light passes once through the color filter in thetransmissive display regions T. Therefore, if the same color filter isused for the reflective display regions R and the transmissive displayregions T, the color of the reflective display is darker than that ofthe transmissive display to deteriorate a chroma balance. However, inthis exemplary embodiment, both the reflective display color filter andthe transmissive display color filter are used, and the chroma of thedye layer 61R of the reflective display color filter is set to be lowerthan that of the dye layer 61T of the transmissive display color filter,thereby enhancing a chroma balance between the display colors of thereflective display and the transmissive display.

Fourth Exemplary Embodiment

A fourth exemplary embodiment of the present invention is describedbelow with reference to FIG. 10.

FIG. 10 is a sectional view showing the schematic construction of aliquid crystal display device of this exemplary embodiment. The liquidcrystal display device of this exemplary embodiment has the same basicconstruction as the first exemplary embodiment, but is different in thatan insulating layer is not provided on a lower substrate. Therefore, inFIG. 10, the components common to those in FIG. 1 are denoted by thesame reference numerals, and a detail description thereof is omitted.

As shown in FIG. 10, a liquid crystal display device 70 of thisexemplary embodiment includes a transflective layer 18 provided on theinner surface of the lower substrate 13, a dye layer 61R of a reflectivedisplay color filter formed on the transflective layer 18, whichcorresponds to the reflective display region R, and a dye layer 61T of atransmissive display color filter formed in the apertures 18 a whichcorrespond to the transmissive display regions T. The dye layer 61R ofthe reflective display color filter is controlled to have lower chromathan that of the dye layer 61T of the transmissive display color filter.This construction is the same as in the third exemplary embodiment.Also, the retardation layer 20 is formed on the dye layer 61R of thereflective display color filter so as to function as a liquid crystallayer thickness controlling layer to decrease the thickness of theliquid crystal layer in the reflective display regions R as comparedwith that in the transmissive display regions T. Furthermore, the pixelelectrodes 23 and the alignment film 24 are laminated in turn on theretardation layer 20. The construction formed on the upper substrate 14is the same as in the first to third exemplary embodiments.

The liquid crystal display device 70 of this exemplary embodiment canexhibit the same effect as the above-described exemplary embodimentwhich is capable of brightening the transmissive display, achieving ahigh contrast display, decreasing the number of components, thinning thedevice, and enhancing a chroma balance between the display colors of thereflective display and the transmissive display in comparison to arelated art display device. Furthermore, in this embodiment, theretardation layer 20 also functions as the liquid crystal layerthickness controlling layer to eliminate the need to form an insulatinglayer separately, thereby simplifying the manufacturing process, forexample, as compared with the third exemplary embodiment.

With respect to the positional relation between the transflective layerand the insulating layer functioning as the liquid crystal layerthickness controlling layer, the transflective layer 18 may be formed onan insulating layer 62, and the retardation layer 20 may be formed onthe transflective layer 18, as shown in FIG. 11. Alternatively, as shownin FIG. 12, the transflective layer 18 and the retardation layer 20 maybe formed on the lower substrate 13 side, and the insulating layer 62may be formed on the upper substrate 14 side.

[Exemplary Electronic Apparatus]

An example of an electronic apparatus including the liquid crystaldisplay device of any one of the above-described exemplary embodiment isdescribed below.

FIG. 4 is a perspective view showing an example of a cellular phone. InFIG. 4, reference numeral 1000 denotes a cellular phone body, andreference numeral 1001 denotes a liquid crystal display part using theliquid crystal display device.

FIG. 5 is a perspective view showing an example of a wristwatchelectronic apparatus. In FIG. 5, reference numeral 1100 denotes a watchbody, and reference numeral 1101 denotes a liquid crystal display partusing the liquid crystal display device.

FIG. 6 is a perspective view showing an example of portable informationprocessors such as a word processor, a personal computer, and the like.In FIG. 6, reference numeral 1200 denotes an information processor;reference numeral 1202, an input part, such as keyboard or the like;reference numeral 1204, an information processor body; and referencenumeral 1206, denotes a liquid crystal display part using the liquidcrystal display device.

Each of the electronic apparatuses shown in FIGS. 4 to 6 includes theliquid crystal display part using the liquid crystal display device ofany one of the above exemplary embodiments to realize an electronicapparatus having a display part capable of achieving a bright display inthe transmission mode.

The technical field of the present invention is not limited to theabove-described exemplary embodiments, and various changes can be madein the scope of the gist of the present invention. For example, in theabove exemplary embodiments, the retardation layer has a retardation ofa quarter wavelength in the reflective display regions, and thethickness of the liquid crystal layer in the transmissive displayregions is twice as large as that in the reflective display regions sothat with the selective voltage applied, the phase shift of the liquidcrystal layer is 0 in both the reflective display regions and thetransmissive display regions, while with the non-selective voltageapplied, the phase shifts of the liquid crystal layer in the reflectivedisplay regions and the transmissive display regions are a quarterwavelength and a half wavelength, respectively. By setting suchconditions, a structure can be formed in which the transmissive displaycan be made brightest, and the contrast can be most enhanced. However,the phase shift of each region is not necessarily set to the aboveconditions. Also, a phase shift may be applied only to at least thereflective display regions, and the phase shift in the transmissivedisplay regions may be greater than that in the reflective displayregions in order to decrease the phase shift in the reflective displayregions. In this construction, the transmissive display can be madebrighter than at least a conventional display device.

Furthermore, in the above-described exemplary embodiments, a positiveliquid crystal is used and aligned horizontally in an initial state sothat with the voltage applied, the phase shift is 0, while with novoltage applied, the phase shifts in the reflective display regions andthe transmissive display regions are a quarter wavelength and a halfwavelength, respectively. However, conversely, a negative liquid crystalmay used and aligned vertically in an initial state so that with novoltage applied, the phase shift is 0, while with the voltage applied,the phase shifts in the reflective display regions and the transmissivedisplay regions are a quarter wavelength and a half wavelength,respectively. Furthermore, a liquid crystal display device is notlimited to a transflective color liquid crystal display device in anactive matrix system according to the above embodiments, and the presentinvention can also be applied to passive matrix-system and monochromedisplay liquid crystal display devices.

EXAMPLES

In order to prove the effect of the present invention, the inventorsactually formed a liquid crystal display device having a constructionaccording to the present invention, and measured transmittance andreflectance. The results are described below.

A liquid crystal display device having a construction according to theexemplary embodiment shown in FIG. 1 was formed as a liquid crystaldisplay device of Example 1. A panel had a construction in which thenumber of dots was 160×(120×3 (RGB)), the dot pitch was 240 μm×(80 μm×3(RGB)), and an aperture serving as a transmissive display region had anarea of 68 μm×22 μm (however, two apertures were formed in one dot).

A liquid crystal display device of Example 2 includes a panel having thesame construction as the liquid crystal display device of Example 1, anda reflective polarizing plate provided on the outer side of a lowerpolarizing plate (corresponding to the liquid crystal display device ofthe second embodiment shown in FIG. 3).

A liquid crystal display device having the same construction as therelated art display device shown in FIG. 7 was formed as a liquidcrystal display device of Related Art Example 1. The construction of apanel was the same as the liquid crystal display device of Example 1.

A liquid crystal display device of Related Art Example 2 includes apanel having the same construction as the liquid crystal display deviceof Related Art Example 1, and a reflective polarizing plate provided onthe outer side of a lower polarizing plate.

The transmittance and reflectance of each of these four samples weremeasured under predetermined conditions. The results are shown in Table1.

TABLE 1 Related Art Related Art Construction Example 1 Example 2 Example1 Example 2 Transmittance (%) 1.4 2.4 4.3 7.5 Reflectance (%) 30 30 3131

Table 1 indicates that the four samples have no significant differencein reflectance, and it is thus said that a liquid crystal display deviceof the present invention exhibits the same level of brightness in areflective display as a Related Art display. On the other hand, incomparison between Comparative Example 1 and Example 1 and betweenComparative Example 2 and Example 2, 1.4% of transmittance in RelatedArt Example 1 increases to 4.3% of transmittance in Example 1, and 2.4%of transmittance in Related Art Example 2 increases to 7.5% oftransmittance in Example 2. Namely, in both Examples 1 and 2, thetransmittance increases by about 3 times. These results prove that theconstruction of the present invention has the effect of reducing orpreventing light passing through a liquid crystal layer from beingabsorbed by an upper polarizing plate, and the effect of permitting there-use of light reflected by the back of a transflective layer, therebybrightening the transmissive display by about 3 times while maintainingthe brightness of the reflective display in comparison to a related artdisplay device.

In comparison between Examples 1 and 2, 4.3% of transmittance in Example1 increases to 7.5% of transmittance in Example 2. These results provethat the utilization efficiency of light emitted from a back light canbe enhanced by inserting the reflective polarizing plate between theback light and the lower polarizing plate, to further brighten thetransmissive display.

As described in detail above, the construction of the present inventioneliminates the need for an upper retardation plate used in a related artdevice, and can thus address or solve the problem of the related artdevice in which about a half of circularly polarized light passingthrough a liquid crystal layer is absorbed by the upper polarizing plateto darken a transmissive display. Also, the present invention has theeffect of permitting the re-use of light reflected by the bottom of atransflective layer to brighten the transmissive display whilemaintaining the brightness of a reflective display. It is also possibleto simplify the structure and thin a liquid crystal display device, ascompared with a related art display device.

1. A liquid crystal display device comprising: a liquid crystal layerinterposed between two opposed substrates; a dot region having atransmissive display region and a reflective display region; a thicknessof the liquid crystal layer in the transmissive display region beinggreater than the thickness in the reflective display region; areflective layer provided at the reflective display region; and aretardation layer provided at the reflective display region of theliquid crystal layer side of one of the substrates, the retardationlayer giving transmitted light a phase shift of about a quarterwavelength, and the thickness of the liquid crystal layer in thetransmissive display regions being about twice as large as the thicknessin the reflective display regions, so that with one of a voltage appliedto the liquid crystal layer and no voltage applied to the liquid crystallayer, the phase shifts of the liquid crystal layer in the reflectivedisplay regions and the transmissive display regions being substantiallyzero, and with the other of a voltage applied to the liquid crystallayer and no voltage applied to the liquid crystal layer, the phaseshifts of the liquid crystal layer in the reflective display regions andthe transmissive display regions being about a quarter wavelength and ahalf wavelength, respectively.
 2. The liquid crystal display deviceaccording to claim 1, further comprising a liquid crystal layerthickness controlling layer provided on the retardation layer, tocontrol the thickness of the liquid crystal layer in the transmissivedisplay regions and reflective display regions.
 3. The liquid crystaldisplay device according to claim 1, the retardation layer functioningas the liquid crystal layer thickness controlling layer to control thethickness of the liquid crystal layer in the transmissive displayregions and reflective display regions.
 4. The liquid crystal displaydevice according to claim 1, the retardation layer being overlapping inthe reflective display region and not overlapping the transmissivedisplay region.
 5. The liquid crystal display device according to claim1, an aperture being opened in the reflective layer, the retardationlayer overlapping the reflective display region and not overlapping theaperture.
 6. The liquid crystal display device according to claim 1, theretardation layer adjusting thickness of the liquid crystal layer in thetransmissive display region to be greater than the thickness in thereflective display region.
 7. The liquid crystal display deviceaccording to claim 6, the retardation layer and the liquid crystal layerthickness controlling layer being disposed on opposite sides of theliquid crystal layer.
 8. The liquid crystal display device according toclaim 6, the liquid crystal layer thickness controlling layer beinglocated in a region corresponding to a region where the reflective layeris disposed.
 9. The liquid crystal display device according to claim 1,further comprising a liquid crystal layer thickness controlling layerthat overlaps the reflective display region, the liquid crystal layerthickness controlling layer controls thickness of the liquid crystallayer to be thicker in the transmissive display region than in thereflective display region.
 10. The liquid crystal display deviceaccording to claim 9, the retardation layer, in addition to the liquidcrystal thickness controlling layer, adjusting thickness of the liquidcrystal layer in the transmissive display region to be greater than thethickness in the reflective display region.
 11. The liquid crystaldisplay device according to claim 9, the retardation layer beingdisposed between the liquid crystal layer and the liquid crystal layerthickness controlling layer.
 12. The liquid crystal display deviceaccording to claim 9, further comprising a color filter disposed betweenthe corresponding substrate and the liquid crystal layer thicknesscontrolling layer.
 13. The liquid crystal display device according toclaim 1, further comprising: a transmissive display color filterdisposed in the transmissive display region; and a reflective displaycolor filter disposed in the reflective display region, the retardationlayer being disposed between the liquid crystal layer and the reflectivedisplay color filter.
 14. The liquid crystal display device according toclaim 13, further comprising a liquid crystal layer thicknesscontrolling layer that controls thickness of the liquid crystal layer tobe thicker in the transmissive display region than in the reflectivedisplay region, the liquid crystal layer thickness controlling layerbeing disposed between the liquid crystal layer and the reflectivedisplay color filter.
 15. The liquid crystal display device according toclaim 1, further comprising a plurality of pixel electrodes, theretardation layer being disposed within a gap between adjacent pixelelectrodes.
 16. The liquid crystal display device according to claim 15,the reflective layer overlapping the gap between adjacent pixelelectrodes.
 17. The liquid crystal display device according to claim 1,further comprising a back light that emits light toward the liquidcrystal layer, the retardation layer being located between the liquidcrystal layer and the back light.
 18. A liquid crystal display devicecomprising: a liquid crystal layer interposed between two opposedsubstrates; a dot region having a transmissive display region and areflective display region; a thickness of the liquid crystal layer inthe transmissive display region being greater than the thickness in thereflective display region; a reflective layer provided at the reflectivedisplay region; a retardation layer provided at the reflective displayregion of the liquid crystal layer side of one of the substrates; atransmissive display color filter disposed in the transmissive displayregion; and a reflective display color filter disposed in the reflectivedisplay region, the retardation layer being disposed between the liquidcrystal layer and the reflective display color filter.
 19. The liquidcrystal display device according to claim 18, further comprising aliquid crystal layer thickness controlling layer that controls thicknessof the liquid crystal layer to be thicker in the transmissive displayregion than in the reflective display region, the liquid crystalthickness controlling layer being disposed between the liquid crystallayer and the reflective display color filter.